how do i make a tank fit.

Published October 3, 2026·File 20 · Fit methods·18 min read

Five ways people get a tank to fit — the men's three-pack, scissors, sizing up, the dryer, a tailor — each one scored on what it actually does to the armhole, what it does to the shoulder line, and whether the garment survives it. With the grade rules and the shrinkage data that decide all five.

There is a whole economy built on this. Thrifted tees and a pair of kitchen scissors. A three-pack bought in a section of the shop you had to decide to walk into. The size up that swims everywhere except the one place you bought it for. The dryer on hot, as a prayer. The tailor you have been meaning to find. People run these methods for years, trade them in comment threads, and refine them into something close to craft — cut the sleeves right below the seam so the shirt doesn't fray is a sentence written by someone who has done it more than twice.

What nobody does is compare them. So here they are, all five, with the garment numbers attached. And the first thing the numbers say is that every one of these methods is aimed at a single measurement, and it is the one measurement that is not printed on any spec sheet you can read before you buy.

What a tank actually has to fit

A tank has fewer places to go wrong than a tee, which is exactly why the places it does go wrong are so loud. There is no sleeve to absorb an error. The armhole is the sleeve. So four measurements decide the whole garment, and they do not have equal weight.

Armhole depth is how far the opening travels down your side from the top of the shoulder. Too shallow and it binds under the arm. Too deep and it opens along the ribs, which is the complaint stated most plainly on the boards: a drop-armhole tank sized for narrow shoulders means any movement puts my sports bra on full display. Armhole opening is the circumference of that hole — how much room the arm has to pass through and rotate in. Shoulder width is the distance between the two points where the strap sits; it is the measurement that decides whether the garment hangs or drags. Chest width is the one everybody talks about, and it is the least decisive of the four, because a knit can stretch across the chest and cannot invent armhole depth it was not drafted with.

Here is the problem in one line. Of those four, the published spec sheet gives you one.

Rows read from the manufacturers' own published charts for two widely printed unisex tanks. Tolerance figure is the stated chest tolerance on the standard cotton tank chart. Not our tech pack.

That last row is worth sitting with. A stated tolerance of ±0.75 inches on chest width means two garments of the same labelled size, both perfectly in spec, can differ by an inch and a half laid flat — three inches of circumference. Which is most of a size. We took that apart at length in why am i a medium here and a large there, and it is the reason "just size up" is advice with a margin of error roughly as large as the thing it is adjusting.

Method 1 — the men's three-pack

This is the oldest answer in the category and the one people are quietest about, because getting it involves a walk across the shop. It also works, partially, for a real reason: a men's block is drafted from a chest-to-shoulder ratio where the shoulder is wide relative to the waist, and the armhole is cut to match. You are not buying a better tank. You are buying a block whose proportions happen to be closer to yours.

What it costs is everything downstream of the armhole. The same block that gives you the shoulder gives you a body width drawn for a chest several inches bigger and a length drawn for a longer torso, so the garment that finally clears your arm hangs off you everywhere else. The full geometry of why that block is shaped the way it is sits in why don't men's shirts ever fit me right, and the three-size version of the same problem is in what's my size, then.

Score: it moves the armhole, keeps the shoulder line, and the garment survives indefinitely. It fails on body width and length, and those are the two failures a tailor can actually fix — which is why these two methods are better used together than alone.

Method 2 — scissors

Be clear about this one: of the five, cutting is the only method that moves the armhole to exactly where you want it. Nothing else on this list does. You are not approximating; you are redrawing the line by hand. The boards have refined it into a real procedure — cut just below the seam so the edge does not fray, use a tank that already fits as the template, take length off the bottom while you are there. That is pattern work with kitchen scissors, and it is the reason this method has survived every trend cycle.

What it costs is structural, and it is worth understanding rather than just being warned about. Two things leave the garment when the sleeve does.

The first is the seam. A set-in sleeve seam is a line of stitching running around a curve, and stitching around a curve is stabilisation — it is the only thing in that area resisting the fabric's pull. Remove it and the shoulder line has nothing holding its shape; the edge becomes free to follow the fabric instead of the pattern.

The second is edge stability, and this is fabric physics rather than sewing. A single jersey — the knit nearly every tee is made from — has a flat face and a looped back, and that asymmetry is exactly why a cut edge rolls. The loop structure is unbalanced and the yarn carries residual torque from spinning, so a free edge curls toward the back face across the width and toward the front face along the length. In a study of curling in single jersey, researchers found the effect scales with yarn twist direction and fabric structure: samples knitted from Z-twist ring-spun yarn curled measurably more than the same fabric in S-twist, and structures carrying tuck stitches curled less [Minapoor and colleagues, Journal of the Textile Institute, 2013]. Nothing you do at the cutting stage changes this, because it is a property of the fabric you already own. It is also why the fix the boards reach for — cut just below the existing seam — is genuinely the right instinct: it leaves the stabilised edge in place and only removes the sleeve beyond it. We took the raw-edge problem apart on its own in why does my cut-off never sit right.

Score: best in class on the armhole, worst in class on reversibility. The shoulder line degrades, the edge moves, and there is no version of this where you put the sleeve back on. For a tee you were going to retire anyway, that trade is close to free. For one you like, it is not.

Method 3 — sizing up

This is the advice you get everywhere, from everyone, and the grade rules say it is the worst trade on the list.

Grading is not scaling. When a pattern goes up a size, every measurement grows, but each one grows by its own fixed increment, set by a grade rule. They are not proportional to each other and they never have been. On the published chart for a widely printed unisex tank, chest grows 2 inches flat per size — about 4 inches of circumference — and body length grows 1 inch. On a basic bodice block drafted to standard practice, the armhole depth grade is 8 millimetres per size and the shoulder width grade is 4 millimetres, against 16 millimetres for chest width.

Read that as a ratio and it is brutal. You are buying about four inches of chest circumference to gain about a third of an inch of armhole depth and about a sixth of an inch of shoulder. The thing you sized up for is the thing that moves least. Everything else moves a lot, which is why the size up solves the binding and immediately creates the tent — and why the people who do it keep describing the result the same way: it fits the shoulders now and swims everywhere below them.

Method 4 — the dryer

The hope here is that heat will take a garment in evenly, like a controlled dial. The data says it does something, just not that, and not where you want it.

A knit is loops. When cotton wets out without tension the fibres swell, the crimp in the loops increases, and the loops move toward the lowest-energy shape available to them, which is round. In Cotton Incorporated's own technical bulletin on shrinkage, that is stated as the whole mechanism: "the rounding of the loop results in a shortening of the loop and therefore relaxation and dimensional change." A round loop is shorter than an elongated one, so the direction that moves is length. In their tumble-drying trials across interlock, single jersey and single pique, "length dimensional changes were always exhibited as shrinkage" — length, every time, every construction [Cotton Incorporated, ISP-1009].

That is the problem in one sentence. On a tank, length is the dimension you need to keep. It is what holds the hem below a waistband instead of riding above it. The armhole is a curve set into the side of the garment; shortening the body does not close it in any controlled way, and it drags the armhole up your side while it goes.

Two further findings from the same document make this worse rather than better. The first: "one cycle may remove around 90% of the total shrinkage available." The dryer trick is not a dial you can turn gradually — it is one move, spent almost entirely the first time, and there is no second pass that gets you the rest. The second kills the technique most people actually use: shrinkage curves were run at 100°F, 150°F and 200°F, and the study reports that "the shrinkage curves and total shrinkage values were identical for all three temperatures commonly encountered in home laundering." Heat is not the lever. What drives the shrinkage is mechanical tumbling once the fabric drops below about 20% moisture content — the point the document calls critical moisture, where relaxation happens fastest. Cranking the dial to hot does not buy you anything the warm setting was not already going to do.

There is a legitimate version of this, and it is the opposite of the trick: wash the thing once the way you intend to wash it forever, then judge the fit. Because roughly nine tenths of the movement happens in that first cycle, the garment you have after one wash is close to the garment you will have in a year. Judging fit on a never-washed tank is judging a measurement that is about to change. The wash-side consequences of that first cycle on colour and surface are in why did this fade so fast.

Method 5 — a tailor

The most underrated of the five, and the most misunderstood, because most people ask a tailor for the wrong operation.

Start with what makes a knit different to work on. A standard straight stitch has no give, so sewn into a stretch fabric it snaps the moment the fabric moves. Sewing a knit properly needs a stitch that travels with it — a zigzag, a twin-needle stretch stitch, or a true coverstitch — and it needs a ballpoint needle, which pushes between the fibres rather than slicing through them the way a sharp needle does. A sharp needle leaves micro-damage that can run later. Thread matters for the same reason: polyester moves with the fabric and cotton thread pops. None of that is exotic, but it is equipment and habit, and a shop set up for suiting may not have either.

Now the operation. Taking in the side seams is a straightforward job on almost any garment. Re-cutting an armhole is not: the opening is finished with a binding or a coverstitched edge, so changing it means unpicking that finish, recutting the curve and re-setting the finish — three operations where the side seam is one, and the last of them needs the machine most alteration shops do not keep.

Which gives you the actual play, and it is the reason this file ranks the way it does. Buy for the armhole, alter for the body. Get the block that clears your arm — that is method 1 — and then have the side seams taken in, which is the easy job. You are using each method for the thing it is good at instead of asking one garment to do both.

The five, ranked

Scored on three things only: whether it moves the armhole, whether the shoulder line survives it, and whether the garment does.

Armhole and shoulder figures are standard bodice-block grade increments, not measurements of a specific garment. Scoring is ours, on the three axes stated.

The 60-second check, before you buy anything

Everything above is argument. This is the part you can use today, and it works because it replaces the measurement nobody publishes with one you take yourself.

You need the tank you already own that works. Not your favourite one — the one that fits. Lay it flat, smooth it out, and take four numbers with a tape:

• Shoulder to shoulder. Across the top, from the outer edge of one strap to the outer edge of the other.
• Armhole depth. From the top of the shoulder seam straight down to the lowest point of the armhole curve.
• Armhole opening. Follow the curve itself from the shoulder point round to the side seam. This is the one that decides whether your arm rotates freely.
• Chest, flat. Side seam to side seam, an inch below where the armhole ends.

Write them down and keep them in your phone. Those four numbers are now your size, and they are more useful than any letter on a label, because two garments labelled the same can legitimately sit three inches of circumference apart under a standard tolerance. When a spec sheet gives you chest and length only — which is most of the time — you at least know the chest number you are looking for, and you know to ask for the other two rather than assume them. Asking a brand for armhole depth is a completely reasonable question, and the answer, or the absence of one, tells you something either way. The longer version of reading charts like this is in which measurement do i actually go by.

And measure it after one wash, not before. Since roughly nine tenths of the available shrinkage comes out in the first cycle, a never-washed garment is measuring a number that is about to move.

Where our own tanks stand

Same rule as every file: what is confirmed gets published, what is not gets said out loud as not.

What we publish on our own pages is real. The London Tank is listed as a structured neckline with closer armhole coverage in COMF+ piqued fabric — 70% modal rayon, 30% recycled polyester, with a fit note that it runs generous and a recommendation to size down between sizes. That last line is there because the drape is deliberate, and a generous drape on a garment drafted at the armhole behaves differently from a generous drape on one that is just big.

Here is the part that is less comfortable to write. Our published charts carry the same two columns as everybody else's. We have spent this entire file arguing that armhole depth and shoulder width are the measurements that decide a tank, and we do not currently publish ours either. We are not going to publish a number we have not measured and logged — that is the rule, and it is the rule precisely so that the numbers we do publish mean something. So this is owed rather than delivered: the measured armhole file, our tanks against the field, taken with a tape and written down. It is on the list. Until it exists, the four numbers above are yours to take, and they work on our garments exactly as well as on anyone else's.

Quick answers

What is the best way to make a tank top fit?

Buy for the armhole and alter for the body. The armhole and shoulder width are the measurements that decide whether a tank hangs correctly, and they are the hardest to change after the fact; chest and body width are the easiest things for a tailor to take in. Buying a block whose armhole clears your arm and then having the side seams taken in beats every single-step method, because side seams are a routine alteration while re-cutting an armhole means unpicking and re-setting a finished edge.

Should I size up to get a tank that fits my shoulders?

It is the most common advice and the worst ratio on the list. On a standard published unisex tank chart, one size up adds 2 inches of flat chest width — about 4 inches of circumference — and 1 inch of body length. Standard bodice-block grade rules move armhole depth by about 8 mm and shoulder width by about 4 mm per size. So you buy roughly four inches of chest to gain about a third of an inch of the thing you actually wanted.

Does putting a tank in the dryer shrink it to fit?

It shrinks the length, not the armhole. In a knit, swollen loops relax toward a round shape, which shortens the loop, and length is the direction that moves — Cotton Incorporated's trials report that length dimensional changes were always exhibited as shrinkage. Two things make it a poor tool: around 90% of the available shrinkage comes out in a single cycle, so it is one irreversible move rather than a dial, and shrinkage curves measured at 100°F, 150°F and 200°F were identical — the heat setting is not what does the work.

Why does a cut-off tee curl at the armhole?

Because single jersey — the knit most tees are made from — has a flat face and a looped back, and that unbalanced loop structure plus residual yarn torque makes any raw edge roll. Research on curling in single jersey found the effect varies measurably with yarn twist direction and fabric structure. Cutting also removes the sleeve seam, which was the only thing stabilising the shoulder line. Cutting just below the existing seam rather than through it keeps the stabilised edge and is why that specific technique circulates.

What measurements should I take before buying a tank?

Four, taken from a tank you already own that fits, laid flat: shoulder to shoulder, armhole depth from the shoulder seam down to the lowest point of the curve, armhole opening along the curve itself, and chest flat an inch below the armhole. Take them after one wash, since most of the shrinkage a garment will ever do happens in that first cycle. Those four numbers do more for you than any size letter, especially given a stated chest tolerance of ±0.75 inches on a standard blank.

Keep reading

• why does the armhole always show everything. — File 01: the geometry underneath every method on this page, drawn out properly
• why does my cut-off never sit right. — File 05: method 2 taken apart on its own, edge by edge
• what's my size, then. — File 02: three parts of you in three different sizes, which is the general case of this file

References

Educational only. Garment figures are published manufacturer specifications and standard pattern-grading increments, not measurements of your body or of a specific garment in your hands. Measure the one you own.

— the Scared But Alive fit desk